New install of homeassistant unable to connect

When I try to connect from a web browser I get cannot connect to server.
I have the home assistant companion app and it finds home assistant but errors object mapper failed to serialise response.
I see no errors in the HA core logs
Ping is between 13 and 16 ms

I am stuck for ideas having flashed 2 different SD cards multiple times and never get beyond this stage so about to give up on HomeAssistant

Very odd.

Unplugged a laptop which was near the ethernet over power line and it then worked